Silicon single crystal semiconductor wafers are sliced from a silicon single crystal semiconductor rod (ingot) and are subjected to various treatments such as thermal oxidation in the device manufacturing process. However, these treatments are liable to cause crystal defects (plane defect) in the surfaces of the wafers. To avoid this problem, Japanese Patent Publication (Kokoku) No. 50-182 teaches that the sliced surface of a silicon single crystal wafer should be oriented such that the sliced surface makes a slight off-angle (2.5 to 15 degrees) with the nearest 100 plane of the crystal.
Hence, a semiconductor wafer thus is caused to have distinctive faces, and only a particular one of the two faces is polished and receives other treatments, so that it becomes necessary to conduct a facial discrimination of the semiconductor wafer, which is not possible by visual examination.
Conventionally, for the purpose of enabling one to visually distinguish the particular face of the wafer from the other face, each semiconductor wafer sliced from a silicon single crystal rod (ingot) is provided with two dissimilar orientation flats (hereinafter only referred to as "OF"), or each semiconductor wafer is provided with notches, a laser mark, or the like which enables one to tell one face from the other of the wafer.
Also, since the direction of and the absolute value of the off-angle of the principal plane (sliced surface) of the semiconductor wafer are required to be within respective predetermined ranges, it is necessary to determine the crystal orientation as well a discriminate the faces of the semiconductor wafer.
However, with the conventional methods of discriminating between the faces of a semiconductor wafer, it is necessary to give physical marking to the wafer which requires expensive marking apparatuses, and thwarts an attempt to totally automatize the discrimination operation for rationalization.
Also, in the conventional practices, the examination and determination of whether or not the off-angle of the principal plane (sliced surface) of the wafer is within the predetermined range was carried out only as the single crystal rod (ingot) is sliced into wafers, and after the slicing, the examination and determination was conducted only with a few sample wafers taken from each lot (consisting of semiconductor wafers from the same single crystal ingot) so that in reality most of the wafers were not inspected. Hence the occurrence of out-of-specification wafers was relatively frequent.
As described so far, the inspection of the semiconductor wafers are conducted during or at the end of the processing of the wafers, and there has been known no apparatus by which all of the wafers are automatically inspected for determination of the orientation of their principal planes.
The present invention was contrived in view of the foregoing problems, and an object of the invention is to provide an apparatus for automatically examining a semiconductor wafer to conduct not only the facial discrimination thereof but also the determination of the crystal orientation thereof with high efficiency and precision.